The temperature of the surface of the world's oceans provides a clear indication of the state of the Earth's climate and weather. The AMSR-E instrument on the Aqua satellite measures the temperature of the top 1 millimeter of the ocean every day, even through the clouds. If the average sea surface temperature for a particular date is subtracted from the measured temperature for that date, the resulting sea surface temperature anomaly can be used to accurately assess the current state of the oceans. The anomaly can serve as an early warning system for weather phenomena and can be used to indicate forthcoming problems with fish populations and coral reef health. In this visualization of the anomaly covering the period from June, 2002, to September, 2003, the most obvious effects are a successive warming and cooling along the equator to the west of Peru, the signature of an El Niño/La Niña cycle. Around January 1, 2003, a cooler than normal region of the ocean appears in this region as part of a La Niña and flows westward, driven by the trade winds. The waves that appear on the edges of this cooler area are called tropical instability waves.